Noun
(nautical) plumb line for determining depth
Source: WordNetlead-line
A recent innovation is the use of a " looping pedal " to record a chord sequence or riff over which the lead line can then be played, simulating the sound achieved by having two guitarists. Source: Internet
In those with a single guitarist, the guitarist may play lead and rhythm at different times or simultaneously, by overlaying the rhythm sequence with a lead line. Source: Internet